U.S. patent number 6,240,921 [Application Number 08/837,672] was granted by the patent office on 2001-06-05 for automated stop/start control in the administration of cpap treatment.
This patent grant is currently assigned to ResMed, Ltd.. Invention is credited to John William Ernest Brydon, Michel Calluaud.
United States Patent |
6,240,921 |
Brydon , et al. |
June 5, 2001 |
Automated stop/start control in the administration of CPAP
treatment
Abstract
Method for automatic stop-start control of a breathing
apparatus. Automatic starting and stopping of the device based upon
the determination of a user wearing the mask by way of proximity
sensors determining that a user is physically in contact with the
mask in order to start the device and stopping the device when the
proximity sensors determine the user is not in physical contact
with the mask.
Inventors: |
Brydon; John William Ernest
(Wollstonecraft, AU), Calluaud; Michel (Ryde,
AU) |
Assignee: |
ResMed, Ltd.
(AU)
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Family
ID: |
3777391 |
Appl.
No.: |
08/837,672 |
Filed: |
April 22, 1997 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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347552 |
Nov 29, 1994 |
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Foreign Application Priority Data
Current U.S.
Class: |
128/205.23;
128/204.18; 128/204.21; 128/205.25 |
Current CPC
Class: |
A61M
16/0051 (20130101); A61M 16/024 (20170801); A61M
16/0069 (20140204); A61M 2016/0039 (20130101); A61M
2039/1005 (20130101); A61M 2205/3561 (20130101); A61M
2205/13 (20130101) |
Current International
Class: |
A61M
16/00 (20060101); A61M 39/10 (20060101); A61M
39/00 (20060101); A62B 007/00 (); A62B
009/00 () |
Field of
Search: |
;128/202.22,204.18,204.21,204.22,204.23,204.24,205.23,205.25 |
References Cited
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|
Primary Examiner: Dawson; Glenn K.
Assistant Examiner: Weiss, Jr.; Joseph F.
Attorney, Agent or Firm: Pillsbury Winthrop LLP
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATION
This application is a divisional of copending application Ser. No.
08/347,552, filed Nov. 29, 1994.
Claims
What is claimed is:
1. A method for controlling an apparatus for the administration of
continuous positive airway pressure (CPAP) treatment, the apparatus
having a controllable flow generator coupled to an air delivery
circuit, in turn coupled to a mask for the supply of CPAP treatment
to a patient's airways, the method comprising the steps of:
determining that the patient is wearing said mask, and if being
worn controlling commencement of the administration of CPAP
treatment by activating said flow generator, said determining steps
comprising:
(a) detecting flow of air in said air delivery circuit;
(b) detecting a pressure change in said air delivery circuit;
and
(c) detecting proximity of the patient's face with said mask.
2. A method for controlling an apparatus for the administration of
continuous positive airway pressure (CPAP) treatment, the apparatus
having a controllable flow generator coupled to an air delivery
circuit, in turn coupled to a mask for the supply of CPAP treatment
to a patient's airways, the method comprising the steps of:
determining that the patient is wearing said mask, and if being
worn commencing the administration of CPAP treatment, said
determining steps comprising:
(a) detecting flow of air in said air delivery circuit;
(b) detecting a pressure change in said air delivery circuit;
and
(c) detecting proximity of the patient's face with said mask,
wherein said detecting flow of air comprises the steps of detecting
a change in pressure drop along at least a portion of said air
delivery circuit, comparing said change in pressure drop against a
threshold, and if said threshold is exceeded it is determined there
is air flow.
3. A method for controlling an apparatus for the administration of
continuous positive airway pressure (CPAP) treatment, the apparatus
having a controllable flow generator coupled to an air delivery
circuit, in turn coupled to a mask for the supply of CPAP treatment
to a patient's airways, the method comprising the steps of:
determining that the patient is wearing said mask, and if being
worn commencing the administration of CPAP treatment, said
determining steps comprising:
(a) detecting flow of air in said air delivery circuit;
(b) detecting a pressure change in said air delivery circuit;
and
(c) detecting proximity of the patient's face with said mask,
wherein said detecting a pressure change comprises the steps of
measuring mask pressure or pressure at a point along said air
delivery circuit, detecting a change in said measured pressure,
comparing said change in pressure against a threshold, and if said
threshold is exceeded it is determined that the mask is being
worn.
4. A method for controlling an apparatus for the administration of
continuous positive airway pressure (CPAP) treatment, the apparatus
having a controllable flow generator coupled to an air delivery
circuit, in turn coupled to a mask for the supply of CPAP treatment
to a patient's airways, the method comprising the steps of:
determining that the patient is wearing said mask, and if being
worn commencing the administration of CPAP treatment, said
determining steps comprising:
(a) detecting flow of air in said air delivery circuit;
(b) detecting a pressure change in said air delivery circuit;
and
(c) detecting proximity of the patient's face with said mask, to
the
wherein said detecting proximity of said mask to the patient's face
comprises the step of detecting a change in electrical
characteristics of circuit means mounted from said mask.
5. The method as claimed in claim 4, wherein said characteristics
of said circuit means include the resistance between two
electrodes, the capacitance between two electrodes, or the
inductance of a coil means.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to automated stop/start control in the
administration of continuous positive airway pressure (CPAP)
treatment.
2. Background of the Invention
The administration of CPAP is common in the treatment of
obstructive sleep apnea (OSA) syndrome and upper airway resistance
syndrome. The fundamental disclosure of CPAP is made in the
specification of International Patent Application No.
PCT/AU82/00063, published under WO 82/03548.
CPAP treatment effectively acts as a pneumatic split of a patient's
upper airways by the provision of a positive air pressure of
approximately 10 cm H.sub.2 O, although pressures in the range of
approximately 5-20 cm H.sub.2 O are encountered. More sophisticated
forms of CPAP, such as bi-level CPAP and autosetting CPAP, are
described in U.S. Pat. No. 5,245,995. Common to all forms of CPAP
is a nose, mouth or face mask fitted to a patient having connection
via an air delivery tube to an air flow generator.
CPAP flow generators are normally switched between a standby or
stop mode to a functional mode in which pressurized air or oxygen
mix is supplied to the patient by a switch located on the body of,
or adjacent to, the flow generator. Alternatively, a cordless radio
or infra-red remote control unit can be operated by the patient at
some distance from the flow generator.
In other cases the control switch (or switches), which may be
electrical or pneumatic, are located in the vicinity of the
patient's mask, and control signals from them are carried back to
the flow generator in parallel with the interconnecting air
delivery tubing. As an alternative to a nose or mouth mask, nasal
prongs (cannulae) may be inserted into the nares to effect a seal
between the air delivery circuit and the patient's airway. In all
cases, the patient must manually depress a control button to
initiate the CPAP treatment.
In this specification the term mask is to be explicitly understood
as embracing a nose mask, mouth mask, nose and mouth mask and nasal
prongs. Furthermore, reference to a mask being worn indicates
sealing engagement with the patient's face or with the entrance to
the nares. In particular, the expression "a mask being worn"
embraces the embodiment of nasal prongs being inserted into the
nares.
There are a number of disadvantages in the known control
implementations described above. Firstly, the patient may have to
reach out of bed to press a control on the flow generator. This may
be difficult to do if they are already wearing the CPAP mask with
its connected tubing, or if the flow generator is some distance
from the bed. Secondly, a cordless remote control can be mislaid,
and its batteries will run down and must be regularly charged or
replaced. In some instances, too, the remote control must be
directed towards the flow generator to function, however, the flow
generator may be difficult to locate in a dark room. Thirdly,
controls incorporated in the mask make it heavier and therefore
less comfortable to wear, perhaps leading to lack of compliance
with the CPAP treatment. Also, they make cleaning and disassembly
more difficult for the patient using CPAP treatment apparatus at
home.
SUMMARY OF THE INVENTION
It is a preferred object of the present invention to make the
control of CPAP treatment, and particularly flow generators,
significantly easier for patients in the start and/or stop
operations.
Therefore, the invention discloses a method for controlling
apparatus for the administration of continuous positive airway
pressure (CPAP) treatment, the apparatus having a controllable flow
generator coupled to an air delivery circuit, in turn coupled to a
mask for the supply of CPAP treatment to a patient's airways, the
method comprising the steps of determining that the patient is
wearing said mask and, if being worn, commencing the administration
of CPAP treatment.
Preferably, the determining step comprises any one or more of the
steps of detecting flow of air in said air delivery circuit,
detecting a pressure change in said air delivery circuit, and
detecting proximity of the patient's face with said mask.
The invention further discloses a method for controlling apparatus
for the administration of continuous positive airway pressure
(CPAP) treatment, the apparatus having a controllable flow
generator coupled to an air delivery circuit, in turn coupled to a
mask for the supply of CPAP treatment to a patient's airways, the
method comprising the steps of determining whether said mask is
being worn by the patient and, if not being worn, ceasing CPAP
treatment.
Preferably, the determining step comprises any one or more of the
steps of detecting airflow in said air delivery circuit in excess
of flow due to maximum CPAP treatment pressure, detecting a
pressure drop in said air delivery circuit below a minimum CPAP
treatment pressure, and detecting an uncontrolled change in
operation of said flow generator.
The invention yet further discloses a method for controlling
apparatus for the administration of continuous positive airway
pressure (CPAP) treatment, the apparatus having a controllable flow
generator coupled to an air delivery circuit, in turn coupled to a
mask for the supply of CPAP treatment to a patient's airways, the
method comprising the steps of determining whether the patient is
wearing said mask and, if being worn, commencing CPAP treatment;
and if not being worn, ceasing CPAP treatment.
The invention yet further discloses apparatus for controlling the
administration of continuous positive airway pressure (CPAP)
treatment, said apparatus having a controllable flow generator
coupled to an air delivery circuit, in turn coupled to a mask for
the supply of CPAP treatment to a patient's airways, and further
comprising means for determining that the patient is wearing said
mask, and means for commencing the administration of CPAP treatment
if the mask is being worn.
Preferably, the apparatus further comprises any one or more of
detection means for detecting flow of air in said air delivery
circuit, detection means for detecting a pressure change in said
air delivery circuit, and detection means for detecting proximity
of the patient's face with the mask. Advantageously, the detection
means can include a differential or static pressure transducer.
Further, the detection means can include electrical circuit means
mounted from said mask, the electrical characteristics of which
change with proximity of the patient's face. The changing
electrical characteristics can include resistance between two
electrodes, capacitance between two electrodes, or the inductance
of a coil means.
The invention further discloses apparatus for controlling the
administration of continuous positive airway pressure (CPAP)
treatment, said apparatus having a controllable flow generator
coupled to an air delivery circuit, in turn coupled to a mask for
the supply of CPAP treatment to a patient's airways, and further
comprising means for determining whether said mask is being worn by
the patient, and means for ceasing CPAP treatment if said mask is
not being worn.
Preferably, the apparatus further includes detecting means for
detecting air flow in said air delivery circuit in excess of flow
due to maximum CPAP treatment pressure, detection means for
detecting a pressure drop in said air delivery circuit continuing
for a predetermined period of time, and detection means for
detecting an uncontrolled change in operation of said flow
generator. The detecting means can include a differential or static
air pressure transducer. Further, the detecting means can include
means for measuring electrical power consumption of said flow
generator, or means for measuring rotational speed of said flow
generator.
BRIEF DESCRIPTION OF THE DRAWINGS
A number of embodiments of the invention will now be described with
reference to the accompanying drawings, in which:
FIGS. 1a and 1b show arrangements for the determination of air flow
rate as an indication of whether a CPAP mask is or is not being
worn;
FIG. 2 shows an arrangement for the determination of a change in
pressure as an indication of whether a CPAP mask is or is not being
worn;
FIGS. 3a, 3b and 3c show arrangements for the determination of the
proximity of a mask to a patient's face;
FIGS. 4a and 4b show further sensor arrangements for the
determination of the proximity of a mask to a patient's face; FIGS.
5a and 5b show schematic control arrangements in the determination
of a CPAP mask not being worn; and
FIG. 6 shows a schematic diagram of an embodiment incorporating
starting and stopping of CPAP apparatus.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENT AND BEST MODE
1. Automatic Start
Embodiments of the present invention offer an improvement in
controlling a CPAP flow generator by determining that the patient
is wearing the CPAP mask (including, as noted above, inserted nasal
prongs) and then starting the flow generator automatically, either
switching to full treatment pressure or into a pressure ramp
controlled by a delay timer. This determination can be achieved in
any one or more of four ways.
The first such technique is the detection of the flow of air in the
breathing (air delivery) circuit caused by the patient breathing.
This is achieved by measurement of a change in the pressure drop
across a flow restriction located in the breathing circuit, either
in the proximity of the mask or the flow generator.
FIG. 1a shows a mask 1 interconnected with a flow generator
(turbine) 4 by a flexible air delivery tube 2. Part-way along the
delivery tube 2 is a flow restriction 3, typically in the nature of
a narrowing of the diameter of the air delivery tube 2 or an iris.
By measurement of the pressure drop (P.sub.1 -P.sub.2) across the
flow restriction 3, the presence of airflow can be detected. The
pressures P.sub.1, P.sub.2 are supplied to the CPAP controller 8 by
respective interconnecting tubes 13, 14. A pressure drop change
value of X cm H.sub.2 O, determined by the CPAP controller 8, is
set as a threshold and if exceeded is taken as indicative of
airflow, and hence that the mask is being worn. Because the sense
of the change in pressure drop will be opposed dependent upon
inspiration or expiration, it is the modulus (or absolute value) of
the pressure change compared against the threshold.
Alternatively, as shown in FIG. lb, the measurement can be of the
change in pressure drop (P.sub.1 -P.sub.2) across substantially the
whole length of the air delivery tube 2 itself. It is then a simple
matter of comparing the modulus of the airflow rate (i.e., pressure
drop having been calibrated against airflow rate) as against a
threshold value (typically 200 ml/s) to determine that the mask 1
is being worn and that it is appropriate to commence the
administration of CPAP treatment. The pressure P.sub.2 also can be
the actual flow generator delivery pressure measured at a point
internally of the casing that houses the control circuits 8 and the
flow generator 4.
It will be apparent that the methods described above may
continually seek to commence the administration of CPAP treatment
when actually being administered due to respiration causing a
change in pressure drop. This, of course, presents no problem in
the control of the CPAP. Furthermore, the automatic stop
embodiments to be described either will override the start command,
else the start command would cease being produced.
A second method of determining that the mask is being worn is by
the detection of a pressure change in the breathing circuit caused
by the patient breathing. As shown in FIG. 2, this is achieved by
the detection of a change of the pressure P.sub.1 (typically a
decrease) in the air delivery tube 2 sensed by a conduit 15
connected with a pressure switch (not shown) located within the
controller 8. This measurement is made in or near the mask 1, but
equally could be at the flow generator 4, and its absolute value is
compared against a threshold of, say, 1 cm H.sub.2 O as an
indication of respiration and thus the mask being worn. In the
alternative, the time varying pressure signal P.sub.1 (t) can be
signal processed to detect the appearance of flow as a slight
negative pressure, say, 1 cm H.sub.2 O as the threshold indicative
of inspiration, as thus indicative of the CPAP mask being worn.
A third method is the detection of the contact with, or close
proximity of, the patient's face with the CPAP mask as determined
via a change in the electrical characteristics of an electrical
circuit having one or more electrodes located in the mask 1. The
electrical characteristic can be a measure of impedance or a change
in capacitive or the inductive coupling of an electrical circuit
connected to the mask. Alternatively, the proximity of the
patient's hand can be sensed as that person picks up the mask, as
this too will affect the capacitance/inductance of the circuit.
As shown in FIGS. 3a-3c, this method is achieved by the location in
or near the mask 1 of two or more electrodes, shown as a pair of
conductive plates 5 in FIG. 3a, capacitive plates 6 in FIG. 3b and
an inductive coiled wire in FIG. 3c. Each one of these types of
electrode typically is connected to the controller 8 by two
interconnecting wires 9. As the mask 1 is brought in proximity to,
or in contact with, the patient's face, the electrical state of the
sensing circuit within the controller 8 will change. The detectable
change is for the reason that a conductive (albeit high resistance)
path is provided by the surface of the patient's face. The change
will either be as a change in surface resistance (FIG. 3a), a
change in capacitance (FIG. 3b) or a change in inductance (FIG.
3c).
A fourth method of determining that the mask is being worn is by
the detection of the contact of the mask with the patient's face,
achieved via an electrical or pneumatic switch located in the mask.
As shown in FIG. 4a, this is achieved by an electric switch 10 (or
switches) located in the mask 1 in such a position as to be
depressed or deformed when the mask 1 is brought into contact with
the patient's face. The change of state of the switch 10 is
therefore detectable by the controller circuitry 8, and thereafter
commences the administration of CPAP treatment. Alternatively, as
shown in FIG. 4b, a sac 11 of gas or liquid is similarly located on
the mask 1 such that contact with the face causes distortion of the
sac, and the concurrent pressure change or volumetric flow in the
connecting tube 12 is detected by a pressure switch or other
suitable device within the controller 8, thus again commencing the
administration of CPAP treatment.
2. Automatic Stop
Embodiments of the present invention offer an improvement in
controlling a CPAP flow generator by determining whether the CPAP
mask is no longer being worn and then switching the flow generator
4 off automatically. This determination can be achieved in any one
or more of three ways.
The first method is by the detection of increased flow of air in
the breathing circuit as a result of the patient's face no longer
blocking the mask air outflow. This is achieved by measurement of a
change in pressure drop across a flow restriction located in the
breathing circuit, either in the proximity of mask 1 or of the flow
generator 4. In other words, it is essentially the same procedure
as applied in the first embodiment of "automatic start," except
that the change in pressure drop is of an absolute value equivalent
to a different (higher) flow threshold, say 3 cm H.sub.2 O
continuing for three seconds or more, is used in the comparison
with the measured airflow. The threshold is greater than the
maximum flow due to the maximum CPAP treatment pressure. The
apparatus of FIG. 1a thus applies as previously described.
Alternatively, the measurement can be of the pressure drop along
the length of all or part of the air delivery tubing itself, again,
similarly as previously described in FIG. 1b. Accordingly,
detection of an increase in airflow rate will cause the controller
8 to stop the administration of CPAP treatment. It may also be the
case that an alarm is sounded in the event that the mask 1 may have
inadvertently come off the patient's face, or other such
occurrence.
A second method is by detecting the drop in pressure in the
breathing circuit in the vicinity of the mask to a low or near-zero
value, and certainly below the minimum CPAP treatment pressure,
caused by the decreased restriction to flow due to the removal of
the patient's face from the mask whilst CPAP treatment is being
administered. This is achieved by the detection of a change of
pressure, typically a decrease to less than 1 cm H.sub.2 O, in the
breathing circuit using a pressure transducer or pressure switch.
Most usually this measurement is made in the mask or near the mask
in the air delivery circuit. Once again, the procedure utilizes
apparatus very similar to that shown in FIG. 2. Upon sensing the
decrease in pressure in excess of the threshold (again, possibly
continuing for 3 seconds or more), the controller 8 will
automatically stop the CPAP treatment.
A third method is by detecting an increase in the speed or the
electrical supply current (power consumption) of the flow generator
4 due to the higher volumetric flow in the breathing circuit where
the mask is not in place. Both instances exemplify an uncontrolled
change in operation of the flow generator. Where the electric motor
driving the CPAP flow generator is regulated in pressure, a sudden
loss of back pressure due to a mask being removed will result in an
increase in rotational speed of the turbine above the rotational
speed for any treatment pressure as the turbine attempts to raise
the mask pressure. For the case where the motor is speed regulated,
the result of a mask being removed is a change (increase) in motor
current below a set point current value in consequence of an
increased flow loading on the flow generator.
FIG. 5a shows the flow generator 4 as a component motor 20 and
turbine 21. The winding(s) of the motor 20 (whether AC or DC) are
supplied by a power supply 22, one interconnecting cable of which
includes a current sensing resistor 23. The motor 20 receives a
control signal 24 supplied from a motor controller 25 that effects
speed control, including stopping and starting of CPAP treatment.
The motor controller 25 also receives, as a speed regulating
feedback signal, an output signal 26 indicative of the motor
speed.
The voltage appearing across the resistor 23 is directly
proportional to current, and this voltage potential is applied to a
differential amplifier 27. The output from the differential
amplifier 27 passes to an averager/integrator circuit 28 that
averages the pseudo-current value, and integrates it over a period
of time to produce a non-linear signal now indicative of power
consumption of the flow generator motor 20. A threshold generator
29 outputs a threshold value to a comparator 30 that also receives
the output of the averager/integrator circuit 28. A comparison then
is made between the threshold and the calculated power consumption
signal, and if the threshold is exceeded, the mask 1 is determined
to have been removed and the comparator 30 outputs a control signal
to the motor controller 25 causing the motor 20 to be stopped,
thus, in turn, stopping the administration of CPAP treatment. The
threshold also may vary as a function of the selected pressure of
the flow generator.
Alternatively, in flow generators where speed is not regulated, as
in the case shown in FIG. 5b, the change in motor speed, typically
detected from the switching signal to one winding or by the output
of a Hall-effect sensor integral within the motor 20 itself, has a
relation with increase in supplied pressure. FIG. 5b shows the
motor speed signal 26 also being supplied to a motor speed
measuring circuit 31. In a similar way as discussed above, the
motor speed is compared with a threshold in the comparator 30, and
if an increase in motor speed above the threshold is determined to
have occurred, then a signal is passed to the motor controller 25
to cause the motor 20 to stop, hence ceasing the administration of
CPAP treatment.
3. Automatic Start and Stop
FIG. 6 shows an embodiment of CPAP apparatus incorporating the
features of both automatic start and automatic stop. Where
convenient, like reference numerals have been used for components
common with the embodiments previously described. The mask pressure
signal P.sub.1 (t) is provided by the tube 13 to a pressure
transducer 40. The transducer 40 generates a differential output
voltage proportional to the mask pressure. The differential
voltages are applied to a buffering amplifier 42, and the output
voltage then is filtered by a filter component 44, resulting in a
voltage signal, the V.sub.p)(t) proportional to the mask pressure.
This voltage is AC coupled by RC circuit 46 to a comparator 48 to
remove any static offset. The comparator 48 then compares the
voltage signal against a threshold value V.sub.1T.
If the mask is being worn and there is respiration, then flow
occurs along the breathing circuit. This then induces a pressure
within the mask, which is reflected in the voltage V.sub.1T, and if
the flow value is above some minimum (determined by the threshold
P.sub.1 (t)) then it is determined that the mask is being worn, in
which case the output of the comparator 48 goes high and causes the
set output of a bistable logic circuit 50 similarly to go high and
signal the motor ON/OFF control circuit 52 in turn to signal the
motor speed control circuit 54 to start the flow generator 4.
The output of the motor speed controller 54 is six gating signals
supplied to a double bridge inverter circuit 56. Thus the flow
generator 4 is an embodiment is a fractional horse power
three-winding brushless synchronous machine.
The flow generator 4 also is provided with a revolution counter,
perhaps in the form of a pulse generator, that provides a
rotational speed signal feedback to the motor speed controller
54.
The motor current line contains a low value resistor, R.sub.sense,
that generates a voltage, V.sub.sense, that is directly
proportional to the motor current. The voltage is passed via a low
pass filter 60 to a comparator 62, where a comparison is made
between the sensed voltage and a further threshold voltage,
V.sub.2T, in order to determine when there is an unexpected
increase in motor current indicative of the mask no longer being
worn. That is, the speed feedback mechanism will operate such that
if the mask no longer is being worn, the motor speed controller 54
will control the turbine 4 such that there will be an increase in
motor current due to an attempt being made to keep the mask
pressure at a constant level. In the case that the motor current
level exceeds that of the threshold, V.sub.2T then the output of
the comparator 62 goes high, and is then coupled by an RC network
64, functioning as a form of timer in accordance with the time
constant RxC. The output of the timer circuit 64 passes via a
buffering threshold circuit 66 that discriminates the logic 0 and 1
levels to the reset input to the bistable circuit 50, in turn
causing the motor ON/OFF control circuit 52 to signal the motor
speed control 54 that the flow generator 4 is to be stopped.
An additional application of these principles is the detection and
quantification of leaks in the breathing circuit, particularly
those between the mask and the patient's face. That is, the motor
power consumption or speed variation can give a confident
indication, below the threshold values described, of the occurrence
of mask leaks and the like. Typically, the quantities vary
non-linearly with flow and are passed through linearising circuitry
(or software) prior to quantification.
The combination of automatic start and stop described above can be
used to provide automatic control of a CPAP flow generator,
starting the machine whenever the mask is being worn, and stopping
it whenever not being worn. This provides advantages for patients
who get up from their beds during the night and for patients who,
because of age (young or old) or physical or mental incapacity,
cannot easily operate manual controls.
Numerous alterations and modifications, as would be apparent to one
skilled in the art, can be made without departing from the broad
scope of the present invention. All such alterations and
modifications are to be considered as within the scope of the
invention, embodiments of which have been hereinbefore
described.
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